An air-traffic controller in Las Vegas became incapacitated during a nightly solo shift – leaving pilots confused as she slurred her words before becoming unresponsive.

The woman, who has not been identified, began her shift at McCarran International Airport about 10 p.m. Wednesday and her instructions appeared to degrade shortly after 11 p.m., according to the Las Vegas Review-Journal.

“Landing at possible … into Las Vegas…,” the controller, who also mixed up the planes’ call signs, could be heard saying in an audio recording of the incident obtained by KVVU-TV.

One of the pilots chimed in, saying: “Is there somebody else that knows what they’re doing?”

A few minutes later, another pilot asked if there’s anyone else to talk to in the tower:

“Sorry, I’m choking a little bit,” said the controller, who was heard coughing.

“I guess somebody is checking with the tower up there. Anybody else in operations? Is there something going on up there?” the pilot said.

“Our ramp controller just advised everybody to call their respective companies to find out what’s going on,” someone was then heard saying from the tower.

Two controllers were on duty at the time of the incident and one was on a break, which is permitted under FAA rules, according to the Review-Journal.

Pilots contacted controllers at the approach control — a separate communications center at the tower — after some of the troubling radio exchanges.

One of the approach controllers alerted the tower controller who was on break of the situation.

“Everybody, just stand by. I’m taking over now. I’ll be right back with you,” another controller said after the stricken woman had communicated with the crews of 29 planes.

The Federal Aviation Administration told CBS News that it “is very concerned about this incident and what occurred is not acceptable.”

On Friday, the agency changed its rules to require two controllers to be in the tower before midnight.

“No safety events occurred during this incident,” the FAA said in a statement about the 40-minute period during which the controller apparently lost consciousness.

Officials did not reveal what caused the controller, who has been placed on leave, to become incapacitated. Medical personnel responded to the tower.

Five inbound plane remained airborne during the incident, and flights on the ground held positions or communicated between themselves to maintain safety while taxiing, according to the FAA.

Rep. Dina Titus, D-Nev., a member of the House subcommittee on aviation, described the incident as “deeply disturbing.”

“The safety of travelers is of paramount concern and I will work with the FAA and McCarran as this investigation continues to unfold,” Titus said in a statement.

The National Air Traffic Controllers Association, which represents more than 14,000 controllers, said it would cooperate with the FAA.

“It is important to remember the outstanding work that is done every day by the thousands of men and women who keep the national airspace system safe,” NATCA President Paul Rinaldi said in a statement.

“Our air traffic controllers in Las Vegas and around the country do an exceptional job day in and day out and demonstrate the highest professional standards.”